Monitoring of sterilant apparatus and method for monitoring sterilant

ABSTRACT

A monitor of the concentration of an oxidative gas or vapor comprises a chemical coupled to a temperature probe, such as by a carrier. Addtionally, the monitor is used in a method of monitoring the concentration of an oxidative gas or vapor and in a sterilization system operated by a user. By utilizing an output signal from the temperature probe to measure the heat produced in an exothermic reaction between the monitored oxidative gas or vapor and the chemical of the monitor, the concentration of the monitored oxidative gas or vapor can be determined. The present invention represents an improvement over the monitors described in the prior art since it is more simplified, and can provide information on the local concentration of an oxidative gas or vapor at various positions within a chamber, and can be operated in size-restricted volumes. Additionally, a method of using the monitor is described, as well as a sterilization system which utilizes the monitor.

FIELD OF THE INVENTION

The invention relates to devices and techniques for monitoring theconcentrations of an oxidative gas or vapor.

BACKGROUND OF THE INVENTION

Medical and surgical instruments have traditionally been sterilizedusing heat (e.g., exposure to steam), or chemical vapors (e.g.,formaldehyde or ethylene oxide). However, both heat and chemicalsterilizations have drawbacks. For example, many medical devices, suchas fiberoptic devices, endoscopes, power tools, etc. are sensitive toheat, moisture, or both. Additionally, formaldehyde and ethylene oxideare both toxic gases which pose potential health risks to healthworkers. After sterilization with ethylene oxide, the sterilizedarticles require long aeration times to remove any remaining toxicmaterial. This aeration step makes the sterilization cycle timesundesirably long.

Sterilization using hydrogen peroxide vapor has been shown to have someadvantages over other chemical sterilization processes (e.g., see U.S.Pat. Nos. 4,169,123 and 4,169,124). The combination of hydrogen peroxidevapor and a plasma provides additional advantages, as disclosed in U.S.Pat. No. 4,643,876. U.S. Pat. No. 4,756,882 discloses the use ofhydrogen peroxide vapor, generated from an aqueous solution of hydrogenperoxide, as a precursor of the reactive species generated by a plasma.The combination of plasma and hydrogen peroxide vapor in close proximitywith the sterilized articles acts to sterilize the articles.

Furthermore, use of low concentrations of hydrogen peroxide vapor hasother advantages when used for chemical sterilization. Hydrogen peroxideis easy to handle, can be stored for long periods of time, isefficacious, and mixes readily with water. In addition, the products ofdecomposition of hydrogen peroxide are water and oxygen, which are bothnon-toxic.

However, there are problems with using hydrogen peroxide forsterilization. First, in order to be effective, devices must be exposedto a specified concentration of hydrogen peroxide. If the concentrationof hydrogen peroxide is not sufficient, the article may require longertime and/or higher temperature to achieve sterilization. Second, if toomuch hydrogen peroxide is present, there is a risk of damaging thesterilized articles, particularly if they contain nylon, neoprene, oracrylic. For hydrogen peroxide absorbent materials, too much peroxidemay leave an unacceptable residue on the sterilized article that may beincompatible with the user or patient. In addition, the use of too muchhydrogen peroxide increases the cost of sterilization. Third, hydrogenperoxide concentration levels can decrease during the course of thesterilization process due to various factors, such as reactions withsome surfaces which are undergoing sterilization, or permeation into andthrough some plastic materials. Fourth, hydrogen peroxide vapor cancondense onto the walls of the sterilization chamber or onto equipmentin the chamber, potentially degrading or harming the equipment. It istherefore important to be able to determine the concentration ofhydrogen peroxide vapor in the sterilization chamber so that enoughhydrogen peroxide is present to be effective, yet not so much that thesterilized articles or other equipment are damaged.

Furthermore, the concentration of hydrogen peroxide vapor can vary fromone section of the sterilized articles to another. Even underequilibrium conditions, there may be regions of the sterilizationchamber which are exposed to higher or lower concentrations of hydrogenperoxide due to restrictions of diffusion caused by other equipment inthe chamber, or by the sterilized articles themselves. In particular, anenclosed volume with only a narrow opening will have a lowerconcentration of hydrogen peroxide than one with a wider opening. Underdynamic conditions (e.g., hydrogen peroxide is introduced into thechamber via an inlet port while at the same time, it is pumped out of anoutlet port), the hydrogen peroxide concentration at a particularposition in the chamber is a function of various factors, including theinlet flow, outlet pumping speed, and geometrical configuration of thesystem's inlet and outlet ports, sterilization chamber, and otherequipment in the chamber, including the sterilized articles.

Various methods for determining hydrogen peroxide concentration levelsin sterilization chambers have previously been disclosed. Ando et al.(U.S. Pat. No. 5,608,156) disclose using a semiconductor gas sensor as ameans for measuring vapor phase hydrogen peroxide concentrations. Thereaction time of the sensor is several tens of seconds, and the relationbetween the sensor output and the concentration of the hydrogen peroxidevapor varies with changes in pressure. Most hydrogen peroxide vaporsterilization procedures involve several treatment steps, usuallyincluding at least one step in vacuum. The response of the sensor tohydrogen peroxide through the treatment steps will therefore change,depending on the pressure used in each treatment step.

Cummings (U.S. Pat. No. 4,843,867) discloses a system for determiningthe concentration of hydrogen peroxide vapor in situ by simultaneousmeasurements of two separate properties, such as dew point and relativehumidity. A microprocessor is then used to fit the two measurements intoa model to calculate the hydrogen peroxide concentration. The methoduses an indirect approximation based on a number of empiricalassumptions, and the accuracy will vary depending on how closely theconditions in the sterilization chamber resemble those used to developthe model. This method also does not yield information concerning thediffering concentrations of hydrogen peroxide at various positionswithin the sterilization chamber.

Van Den Berg et al. (U.S. Pat. No. 5,600,142) disclose a method of usingnear-infrared (NIR) spectroscopy to detect hydrogen peroxide vapor.Hydrogen peroxide has an absorption peak at about 1420 nm (nanometers)which can be used to determine its concentration. However, water isalways present when hydrogen peroxide is present, since water is adecomposition product of hydrogen peroxide. Because water also absorbsnear-infrared radiation at 1420 nm, it interferes with the determinationof the hydrogen peroxide concentration. In order to correct for thisinterference, the water vapor concentration is determined separately byan absorption measurement at wavelengths which hydrogen peroxide doesnot absorb. This measured water vapor concentration is then used tocorrect the absorbance at 1420 nm for the contribution due to water.However, this correction measurement also suffers from contributions dueto contaminants, such as various organic molecules, which absorb in thespectral region of the correction measurement. Since one does notnormally know what organic molecules are present, the correction factoris therefore somewhat unreliable.

Furthermore, the NIR method requires absorption measurements at twodifferent wavelengths and making corrections for the presence of watervapor, organic contaminants, or both. The electronic equipment for doingthese corrections is complex and expensive, and the correction for thepresence of organic compounds is subject to error. Additionally, thecalculated hydrogen peroxide concentration is an average concentrationover the volume which absorbs the near-infrared radiation, not alocalized measurement of concentration at particular positions withinthe sterilization chamber.

U.S. Pat. No. 4,783,317 discloses an apparatus for monitoring theconcentration of hydrogen peroxide in liquid media, e.g. aqueoussolutions for scrubbing the flue gases emanating from waste-incinerationplants or large capacity firing systems. By exploiting the exothermicreaction of hydrogen peroxide with reducing agents (e.g. gaseous sulfurdioxide), the apparatus is able to measure the concentration of hydrogenperoxide in the liquid medium. The U-shaped apparatus comprises athermally insulated measuring cell, a supply line which supplies apartial stream of the liquid from the source to the measuring cell, anda discharge line which returns the liquid to the source. In themeasuring cell, the liquid is combined with a small stream of a reducingagent from a separate supply line, and the temperature of the mixture ismonitored by a sensor. By comparing this temperature to the temperatureof the liquid prior to entering the measuring cell, the apparatusmeasures temperature rise due to the ongoing exothermic reaction whichis a function of the concentration of hydrogen peroxide in the liquid.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides an apparatus formonitoring the concentration of an oxidative gas or vapor comprising: achemical which reacts with the oxidative gas or vapor to produce a heatchange, and a temperature probe which measures the heat change. Thechemical is coupled to the temperature probe, such as through a carrier.Preferred carriers include vacuum grease, tape, epoxy, or silicone. Thecarrier can also comprises a gas-permeable pouch or gas-impermeableenclosure with at least one hole.

In another aspect, the apparatus described above can form part of asterilization system with a control system to produce a desired level ofoxidative gas or vapor. The sterilization system ordinarily comprises: achamber, a door, and a source of oxidative gas or vapor.

In still another aspect, the present invention provides a method ofmonitoring the concentration of an oxidative gas or vapor comprising:providing a chemical which undergoes a reaction with the oxidative gasor vapor to be monitored so as to produce a heat change, providing atemperature probe which detects the heat produced by the reactionbetween the chemical and the oxidative gas or vapor to be monitored andwhich produces an output signal which is a function of the concentrationof the oxidative gas or vapor. The chemical coupled to the temperatureprobe is exposed to the oxidative gas or vapor, and the output signalfrom the temperature probe is measured so as to determine theconcentration of the oxidative gas or vapor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D, and 1E schematically illustrate various preferredembodiments of the present invention comprising a carrier, a chemical,and a temperature probe.

FIG. 2 schematically illustrates a sterilization system utilizing onepreferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1A, 1B, 1C, 1D, and 1E illustrate embodiments of the presentinvention. In a preferred embodiment of the present invention, aconcentration monitor 10 comprises a carrier 12, a chemical 14, and atemperature probe 16. All of the elements of the concentration monitor10 must be compatible with its operating conditions. For use in asterilization system utilizing hydrogen peroxide vapor with or withoutplasma, the carrier 12, chemical 14, and temperature probe 16 must allbe compatible with operations under sterilization conditions and withexposure to hydrogen peroxide vapor and plasma. Persons skilled in theart recognize that there is a wide variety of materials and structureswhich can be selected as the carrier 12 in these preferred embodiments.The carrier 12 couples the chemical 14 in close proximity to thetemperature probe 16 so as to minimize the thermal losses between them.Examples of adequate carriers include, but are not limited to, vacuumgrease, tape, epoxy, or silicone. Additionally, the carrier 12 caneither be configured to expose the chemical 14 directly to theenvironment, or to enclose the chemical 14 in a gas permeable pouch,such as Tyvek tubing, or a gas impermeable enclosure with a hole orholes. In certain embodiments, the chemical can be coupled directly tothe temperature probe without use of a carrier. For example, thechemical 14 can be formed as an integral part of the temperature probe16 or, if the chemical 14 is sufficiently adhesive, it can be directlycoupled to the probe 16.

The chemical 14 is a chemical compound which undergoes an exothermicreaction with the oxidative gas or vapor to be monitored, producing adetectable amount of thermal energy (i.e., heat) upon exposure to theoxidative gas or vapor to be monitored. Persons skilled in the art areable to choose an appropriate chemical 14 which yields a sufficientamount of heat upon exposure to the relevant range of concentrations ofthe oxidative gas or vapor to be measured. Examples for use in ahydrogen peroxide sterilization system include, but are not limited to,potassium iodide (KI), catalase, magnesium chloride (MgCl₂), iron (II)acetate, and platinum on alumina. In addition, a combination of thesechemical compounds may be chosen as the chemical 14. Furthermore,persons skilled in the art are able to select the appropriate amount ofchemical 14 to yield a sufficient amount of heat upon exposure to therelevant range of hydrogen peroxide concentrations.

Various configurations are compatible with use in the preferredembodiments illustrated in FIGS. 1A, 1B, 1C, 1D, and 1E. FIG. 1A shows atemperature probe 16 coated with a thin layer of carrier 12, such asvacuum grease, double-sided tape, epoxy, or silicone, on the tip of theprobe 16 and the chemical 14 is coated on the outside of the carrier 12.FIG. 1B shows the chemical 14 is mixed with the carrier 12 and appliedonto the tip of the temperature probe 16. For example, the chemical isdispersed in the silicone, such as polydimethyl siloxane or othersimilar two-part silicone, prior to curing. The probe 16 is thendip-coated with the chemical-containing silicone. The siliconecontaining the chemical 14 that has been dip-coated onto the probe 16 isthen cured at conditions consistent for two-part silicones. The chemical14 is accessible for reaction as the hydrogen peroxide diffuses into thesilicone matrix. FIG. 1C show the chemical 14 is enclosed onto the tipof the temperature probe 16 with a carrier 12. The carrier 12 is agas-permeable Tyvek pouch with a heat-sealed area 17. The carrier 12 canalso be a gas-impermeable film, or CENTRAL SUPPLY ROOM (“CSR”) wrappouch, or any enclosure with one or more holes to allow the diffusion ofgas or vapor to react with the chemical 14 retained in the enclosure.FIG. 1D shows a chemical 14 coupled to a heat-conducting material 18with a carrier 12, and the heat-conducting material 18 is coupled to thetemperature probe 16 with a substrate 19. The substrate 19 can be tape,adhesive, or any other coupling means. The heat-conducting material 18can be metallic wire or any other materials which can properly conductheat to the temperature probe 16. FIG. 1E show a chemical 14 coupled toa temperature probe 16 with a carrier 12, and two parts of thetemperature probe 16 can be connected and disconnected with a maleconnector 20 and a female connector 21.

The temperature probe 16 is a device which measures the temperature at aparticular location. One preferred embodiment of the present inventionutilizes a fiber-optic temperature probe, such as a Luxtron 3100fluoroptic thermometer, as the temperature probe 16. This fiber-optictemperature probe is coated with Teflon and therefore is very compatibleto any oxidative gas or vapor. Another preferred embodiment utilizes atemperature probe 16 which is a thermocouple probe which utilizes ajunction of two metals or alloys. The thermocouple junction produces avoltage which is a known function of the junction's temperature.Measurements of this voltage across the thermocouple junction cantherefore be converted into measurements of the junction's temperature.Thermocouple junctions can be made quite small (e.g., by spot weldingtogether two wires of 0.025-millimeter diameter composed of differingalloys), so they can be positioned into size-restricted volumes. In yetanother preferred embodiment, a thermistor can be used as a temperatureprobe 16.

Table 1 illustrates the increases of temperature measured by aconcentration monitor 10 with potassium iodide (KI) as the chemical 14.The tip of the fiber-optic temperature probe was first coated with athin layer of Dow Coming high vacuum grease (part number 2021846-0888).About 0.15 grams of KI powder was then applied onto the vacuum grease.This configuration is the same as illustrated in FIG. 1A. Themeasurements were conducted by suspending the concentration monitor 10in a vacuum chamber heated to 45° C., evacuating the chamber, recordingthe initial probe temperature, injecting hydrogen peroxide into thechamber, recording the temperature after all hydrogen peroxide wasvaporized, evacuating the chamber to remove the hydrogen peroxide, andventing the chamber. The measurements were repeated with differentconcentrations of hydrogen peroxide injected into the chamber. The sametemperature probe 16 was reused for all the measurements, and theresults are shown in Table 1. As can be seen from Table 1, KI produces ameasurable increase of temperature with increasing concentration ofhydrogen peroxide. Additionally, this concentration monitor 10 can bereused many times.

TABLE 1 Concentration of H₂O₂ (mg/L) Temperature increase (° C.) 0.2 3.00.4 8.3 0.8 19.2 1.3 24.2 2.1 33.7

Table 2 provides data on the measured temperature increases with varyingconcentrations of hydrogen peroxide for a concentration monitor 10utilizing different chemicals 14. Same test conditions and probeconfigurations were used in these temperature measurements. As can beseen from Table 2, each of the chemicals produced a measurabletemperature rise which increased with increasing hydrogen peroxideconcentration.

TABLE 2 Temperature increase (° C.) Chemical 0.4 mg/L 1.0 mg/L 2.1 mg/LPlatinum on Alumina 13.5 17.2 — Catalase 1.1 — 6.9 Iron (II) acetate62.5 83.1 — Magnesium Chloride 0.8 — 4.4

The utility of using a thermocouple junction as the temperature probe 16is illustrated in Table 3. For these measurements, the concentrationmonitor 10 was configured as illustrated in FIG. 1A. The test conditionsof Table 1 were also used for these measurements. Table 3 illustratesthat significant temperature increases were also observed using athermocouple temperature probe.

TABLE 3 Concentration of H₂O₂ (mg/L) Temperature increase (° C.) 0.2 2.70.4 11.9 0.8 19.3 2.1 24.2

The utility of using double-sided tape as the carrier 12 is illustratedby Table 4, which presents the temperature increases measured by afiber-optic temperature probe 16. A thin layer of 3M Scotch double-sidedtape was first applied to the tip of the fiber-optic probe 16. About0.15 grams of KI powder was then coated onto the tape. Table 1 testconditions were repeated for these measurements. It is apparent fromTable 4 that measurable increases of temperature were detected forincreasing H₂O₂ concentration when using double-sided tape as thecarrier 12.

TABLE 4 Concentration of H₂O₂ (mg/L) Temperature increase (° C.) 0.4 9.31 16.8 2.1 31.2

The utility of using epoxy as the carrier 12 is illustrated by Table 5,which presents the temperature increases measured by a fiber-optictemperature probe 16. The concentration monitor 10 was constructed byapplying a thin layer of Cole-Parmer 8778 epoxy on an aluminum wire.About 0.15 grams of KI powder was then applied and dried onto the epoxy.Finally, the aluminum wire was attached to the temperature probe 16.Table 1 test conditions were repeated for these measurements. It isapparent that measurable increases of temperature were detected forincreasing H₂O₂ concentration when using epoxy as the carrier 12.

TABLE 5 Concentration of H₂O₂ (mg/L) Temperature increase (° C.) 0.4 7.81 12.9 2.1 20.1

The utility of using an enclosure as the carrier 12 to enclose thechemical 14 is illustrated by Tables 6 and 7, which illustrate theincrease of temperature detected by a fiber-optic temperature probe 16with KI contained in an enclosure. For Table 6, the enclosure was PVCshrink tubing with holes. The holes were small enough to trap the KIpowder but large enough to allow the diffusion of gas or vapor into thePVC tubing. For Table 7, the enclosure was gas-permeable Tyvek tubingfabricated from heat-sealed 1073B Tyvek. The inner diameter of theenclosure was about 0.5 centimeters, and its length was approximately1.5 centimeters. For Table 6, about 0.2 grams of KI powder was enclosedin the PVC tubing and the concentration monitor 10 was re-used for allmeasurements. For Table 7, about 0.2 grams of KI powder was enclosed inthe Tyvek pouch and the concentration monitor 10 was also re-used forall measurements. Table 1 test conditions were used for thesemeasurements. It is apparent that measurable increases of temperaturewere detected for increasing H₂O₂ concentration when using bothembodiments of a gas-permeable pouch as the carrier 12. The results alsodemonstrate that the concentration monitor 10 can be re-used and themeasurements are reproducible.

TABLE 6 Concentration of Temperature increase (° C.) H₂O₂ (mg/L) Trial#1 Trial #2 Average 0.2 1.1 1.1 1.1 0.4 9.5 8.8 9.2 1.0 13.6 13.6 13.6

TABLE 7 Concentration of Temperature increase (° C.) H₂O₂ (mg/L) Trial#1 Trial #2 Average 0.4 9.7 8.4 9.1 1.0 17.3 16.8 17.1 1.4 23.6 23.623.6

FIG. 2 schematically illustrates a sterilization system 25 utilizing onepreferred embodiment of the present invention. The sterilization system25 has a vacuum chamber 30 with a door 32 through which items to besterilized are entered into and removed from the chamber 30. The door isoperated by utilizing a door controller 34. The vacuum chamber also hasa gas inlet system 40, a gas outlet system 50, and a radio-frequency(rf) system 60. Comprising the gas inlet system 40 is a source ofhydrogen peroxide (H₂O₂) 42, a valve 44, and a valve controller 46. Thegas outlet system 50 comprises a vacuum pumping system 52, a valve 54, avalve controller 56, and a vacuum pumping system controller 58. In orderto apply radio-frequency energy to the H₂O₂ in the vacuum chamber 30,the rf system 60 comprises a ground electrode 62, a powered electrode64, a power source 66, and a power controller 68. The sterilizationsystem 25 is operated by utilizing a control system 70 which receivesinput from the operator, and sends signals to the door controller 34,valve controllers 46 and 56, vacuum pumping system controller 58, andpower controller 68. Coupled to the control system 70 (e.g., amicroprocessor) is the concentration monitor 10, which sends signals tothe control system 70 which are converted into information about theH₂O₂ concentration in the vacuum chamber 30 at the location of theconcentration monitor 10. The sterilized article 80 is shown to bepositioned in the chamber 30 with concentration monitor 10 located inthe load region to monitor the concentration of hydrogen peroxide in theload region. Persons skilled in the art are able to select theappropriate devices to adequately practice the present invention.

The heat produced between the oxidative gas or vapor and the chemical 14may not be the same for different configurations of the concentrationmonitor 10, carrier 12, and chemical 14. Therefore, for a given type ofconcentration monitor 10, a calibration curve needs to be established todetermine the relationship between the concentration of oxidative gas orvapor and the heat produced. Once the calibration curve is established,the heat detected during the measurement can be converted to theconcentration of the oxidative gas or vapor around the monitor 10.

By coupling the operation of the sterilization system 25 with the H₂O₂concentration measured by the concentration monitor 10, thesterilization system 25 is assured of operating with an appropriateamount of H₂O₂ in the region of the articles to be sterilized. First, ifthe H₂O₂ concentration is determined to be too low for adequatesterilization, the control system 70 can signal the inlet valvecontroller 46 to open the inlet valve 44, thereby permitting more H₂O₂into the chamber 30. Alternatively, if the H₂O₂ concentration isdetermined to be too high, the control system 70 can signal the outletvalve controller 56 to open the outlet valve 54, thereby permitting thevacuum pumping system to remove some H₂O₂ from the chamber 30.Furthermore, if the sterilization system is being operated in a dynamicpumping mode (i.e., H₂O₂ is introduced into the chamber 30 via the inletvalve 44 while at the same time, it is pumped out via the outlet valve54), then either the inlet valve 44 or the outlet valve 54, or both canbe adjusted in response to the measured H₂O₂ concentration to ensure anappropriate level of H₂O₂.

Because the concentration monitor 10 provides localized informationregarding the H₂O₂ concentration, it is important to correctly positionthe concentration monitor 10 within the sterilization chamber 30. Insome preferred embodiments, the concentration monitor 10 is fixed to aparticular position within the sterilization chamber 30 in proximity tothe position of the sterilized articles 80. In other preferredembodiments, the concentration monitor 10 is not fixed to any particularposition within the sterilization chamber 30, but is placed on or nearthe sterilized article 80 itself. In this way, the concentration monitor10 can be used to measure the H₂O₂ concentration to which the sterilizedarticle 80 is exposed. In particular, if the sterilized article 80 has aregion which is exposed to a reduced concentration of H₂O₂ due toshadowing or a reduced opening, then the concentration monitor 10 can beplaced within this region to ensure that a sufficient H₂O₂ concentrationis maintained to sterilize this region. The small size of theconcentration monitor of the present invention permits the concentrationmonitor to be placed in very restricted volumes, such as the innervolume of a lumen, or in a container or wrapped tray. In still otherembodiments of the present invention, a plurality of concentrationmonitors 10 can be utilized to measure the H₂O₂ concentration at variouspositions of interest.

This invention may be embodied in other specific forms without departingfrom the essential characteristics as described herein. The embodimentsdescribed above are to be considered in all respects as illustrativeonly and not restrictive in any manner. The scope of the invention isindicated by the following claims rather than by the foregoingdescription. Any and all changes which come within the meaning and rangeof equivalency of the claims are to be considered within their scope.

What is claimed is:
 1. An apparatus for monitoring the concentration ofan oxidative gas or vapor in a vacuum chamber, the apparatus comprising:a chemical compound which reacts non-catalytically with the oxidativegas or vapor in the vacuum chamber to produce a heat change; and atemperature probe positionable in the vacuum chamber, wherein thechemical compound is coupled to the temperature probe and thetemperature probe is capable of producing an output signal which is afunction of the heat change.
 2. The apparatus as defined in claim 1,additionally comprising a carrier which couples the chemical compound tothe temperature probe.
 3. The apparatus as defined in claim 1, whereinthe oxidative gas or vapor comprises hydrogen peroxide.
 4. The apparatusas defined in claim 2, wherein the carrier comprises vacuum grease,tape, epoxy, or silicone.
 5. The apparatus as defined in claim 2,wherein the carrier comprises a gas-permeable pouch or gas-impermeableenclosure with at least one hole.
 6. The apparatus as defined in claim5, wherein the gas-permeable pouch comprises Tyvek or Central SupplyRoom (“CSR”) wrap.
 7. The apparatus as defined in claim 1, wherein theapparatus further comprising a heat conductor between the chemical andthe temperature probe.
 8. The apparatus as defined in claim 1, whereinthe chemical comprises potassium iodide (KI), magnesium chloride(MgCl₂), or iron (II) acetate.
 9. The apparatus as defined in claim 1,wherein the temperature probe further comprising a connector to connectand disconnect a portion of the temperature probe coupled to thechemical to a remaining portion of the temperature probe.
 10. Theapparatus as defined in claim 9, wherein the temperature probe is afiber-optic temperature probe, a thermocouple probe, or a thermistor.11. A method of monitoring the concentration of an oxidative gas orvapor in a vacuum chamber, the method comprising: providing a chemicalwhich undergoes a non-catalytic reaction with the oxidative gas or vaporin the vacuum chamber, thereby producing a heat change; providing atemperature probe which detects the heat change produced by thenon-catalytic reaction between the chemical and the oxidative gas orvapor to be monitored and which produces an output signal which is afunction of the heat change; positioning the temperature probe in thevacuum chamber; exposing the chemical coupled to the temperature probeto the oxidative gas or vapor; producing an output signal which is afunction of the heat change produced by the chemical; and measuring theoutput signal from the temperature probe.
 12. The method as defined inclaim 11, wherein the oxidative gas or vapor comprises hydrogenperoxide.
 13. The method as defined in claim 11, wherein the carriercomprises vacuum grease, tape, epoxy, or silicone.
 14. The method asdefined in claim 11, wherein the carrier comprises a gas-permeable pouchor gas-impermeable enclosure with at least one hole.
 15. The method asdefined in claim 11, wherein the chemical comprises potassium iodide(KI), magnesium chloride (MgCl₂), or iron (II) acetate.
 16. Asterilization system operated by a user, wherein the sterilizationsystem comprises: a chamber; a door in the chamber; a source ofoxidative gas or vapor in fluid connection with the chamber; a chemicalconcentration measuring system comprising at least one apparatusaccording to claim 1; and a control system which receives input from thechemical concentration measuring, system to produce a desiredconcentration of said oxidative gas or vapor.
 17. The system as definedin claim 16, wherein the system further comprises a pumping system toreduce the pressure in the chamber.
 18. The system as defined in claim16, wherein the oxidative gas or vapor comprises hydrogen peroxide. 19.The apparatus as defined in claim 1, wherein the output signalcorresponds to the concentration of the oxidative gas or vapor at thelocation.
 20. The apparatus as defined in claim 1, wherein the oxidativegas or vapor is in an equilibrium condition.
 21. The method as definedin claim 11, further comprising determining the concentration of theoxidative gas or vapor based on the output signal.
 22. The apparatus asdefined in claim 1, wherein the temperature probe is movable and capableof measuring the temperature at a particular location within the vacuumchamber, and producing an output signal which is a function of thetemperature.
 23. The method as defined in claim 11, additionallycomprising moving the temperature probe to a particular location withinthe vacuum chamber, and producing an output signal which is a functionof the temperature at that location.